MONTPELIER — The dismissal of a drunken driving charge against a Vermont woman detained by two border agents on a state road not far from the Canadian border highlights the growing federal role in state law enforcement, the woman’s lawyer says.

Defense Attorney David Sleigh says such cases are becoming more common because there are more federal agents working along the border. They have broad power to enforce federal law, but they also regularly assist in state cases.

“It limits what might otherwise be unfettered search and seizure powers of Border Patrol agents and limits their authority to the confines of state law,” Sleigh said of last month’s ruling dismissing the charges against his client. “Without this decision a Border Patrol could say, `I want to stop this car for any reason or no reason because I can and hold it because there might be a state law violation.”’

The case began on June 7, when a uniformed Customs and Border Protection officer on his way to work at the border noticed a car parked by the side of the road in Newport with the driver apparently asleep inside. The driver, Meaghan Leary, 29, of Derby, told the agent she was not in distress and didn’t need help.

Yet the agent took her keys and demanded identification. The officer then called a Border Patrol agent, who arrived a short time later. The two agents kept Leary there until a state trooper arrived and arrested her on a DUI charge.

On Aug. 20 Vermont Superior Court Judge Howard Van Benthuysen dismissed the charge because he ruled the agents did not have the grounds to detain Leary and there was no suspicion Leary had committed a federal crime.

Orleans County State’s Attorney Alan Franklin said Friday he wouldn’t appeal. He said the circumstances surrounding the case were unique and would be unlikely to apply in other cases.

“There are enough distinguishing factors that this incident seems to be an anomaly in the things we get from Border Patrol or the customs guys,” Franklin said.

Sleigh says there have been similar cases in other parts of the country. He pointed to a case decided by the 9th U.S. Circuit Court of Appeals in California in which the court dismissed drug charges against a man stopped by Border Patrol agents 70 miles north of the Mexican border on the grounds the agents didn’t have the authority to stop him.

Customs and Border Protection spokeswoman Shelbe Benson-Fuller didn’t respond directly to the circumstances of the Leary case, but she said the agency is committed to ensuring public safety in the areas where its agents operate.

“We have and will continue to work diligently with law enforcement partners at all levels in securing our borders, reducing crime and improving the quality of life in our communities on both sides of the border,” she said in an emailed statement.

In many states, border agents are given state law enforcement authority. In Vermont, federal agents can be certified as state officers if they complete a course at the Vermont Police Academy and are certified by the commissioner of Public Safety.

It’s unclear if the agents who detained Leary had that certification.

Customs and Border Protection agents regularly help enforce state laws along the border. In many cases along remote sections of the border, Border Patrol agents are the first to arrive at the scenes of accidents or crimes.